Condensing the reasons to buy Bitcoin into one is quite a challenge. You should be aware that Bitcoin has a range of use-cases which make the fiat/monetary system obsolete, and is economically superior in many ways.

I'll choose the supply argument as the single reason to provide to you.

Every day, billions/trillions of dollars are created within the global monetary system, increasing its supply and devaluing the money that everyone uses for their day to day purchases. This is even more relevant in this time of global inflation, which is not projected to stop any time soon.

Bitcoin, on the other hand, only distributes new Bitcoin to miners on an average of every 10 minutes (in return for securing the network/ledger by validating new transactions). Every 4 years the reward distributed to miners is halved, and the total amount of Bitcoin that can ever exist is capped at 21,000,000.

The more money that is created globally, the less it is worth. The more economic trouble that countries find themselves in (usually due to large government debt and absurd interest owed to banks), the more they will print (or, the more that banks will lend to governments to pay the interest that (sadly ironically) governments owe to banks).

I am sure that you can see the flaw in the monetary system in comparison to the Bitcoin ecosystem just in this post alone and why Bitcoin is poised to increase in monetary value due to the supply of both systems alone.

You should Do Your Own Research for your own investment. Bitcoin is the top cryptocurrency which means Bitcoin is the best investment choice if you will enter cryptocurrency. You can't appreciate our suggestion if you didn't conduct research by yourself since you don't have an idea about the general overview of crypto. But the main feature of Bitcoin that makes it the number cryptocurrency is it's the only crypto that is truly decentralized since it's 100% controlled by the community which even Satoshi can't gonna give an impact on if ever he wants to manipulate it, unlike other crypto project which is on the palm of a team member.

Bitcoin has a limited supply. And most importantly Bitcoin is Bitcoin!

I am not here to convince you, but one of the reasons why other people buy it is because of its price. It is your job as an investor to figure out why, and if you are also ready for consequences, we ain't like those influencers telling you to buy it now as you could be very rich with it. We are here to tell you that it is very stressful, and you could lose it all if you do it with just hype and not doing your own research.

You can turn your fiat into digital fiat but it will still not get your food or homes, invest in farm land instead it is all going to 0.

If you not convinced to invest in Bitcoin, just don't. If you force yourself to buy Bitcoin, when the price is decrease and it's not like something you've predict, you will say Bitcoin is scam and manipulated by whales.

You can start to learn about Bitcoin and it's feature, there are many videos, books or articles discuss about Bitcoin. After you already understand the basic, you can read the Bitcoin whitepaper. If you still not convinced to invest in Bitcoin, Bitcoin isn't for you then.

If you need a reason to buy I am sure you also need a reason to hold bitcoin when you buy it, and instead of asking you should actually find out for yourself. Everyone will tell you a benefit but in truth nobody cares about you if you invest or not, it is for your own good in the end if you make profit (can also be bad for you). We can only suggest you invest and tell you the benefit but it is left for you to decide to be a beneficiary or not. In the end if it turns out true and all the benefits people mentioned including that of your friend starts becoming a reality, and you just decided that you were not convinced enough even after all the reasons, you will regret it, and it will be your own regret and story.

If you are not convinced on what your friend mentioned to you, then it is now your responsibility to do your respective research about BTC investment. Again, you should not blindly follow others just because they told you so- make your own discretion and judgement before you do anything else.

Personally, one should at least own an investment in BTC due to its potential value in the future. By basing it purely on its price history index, you can see that the price of BTC had increased more than 1000% from its initial price when it first started way back in 2009.

I do believe that BTC is the future of transactions- people would utilize the information given in a public ledger for transparency and BTC would be the currency for it.

indeed many say that in the future the price of bitcoin will be high, so your friends invite you or give advice whether you want to invest in btc or not? and your friend is certainly not wrong, unless he forces you to invest in new btc it is a mistake.

but in this case it's up to you whether you want to invest or not, because investing in btc shouldn't be forced.

there are many reasons that you will get from here, and many people will say the same as what your friends say, but investing in bitcoin requires strong faith and patience, and understanding of the risks that will be faced in the future, such as prices falling by up to 50% from ATH even more, be patient waiting for the new ATH
so understand the basics about btc and you can come back any time to invest in bitcoin and other crypto
but my advice is that you better buy btc first then other crypto when you already benefit from btc itself