Just to invest in Bitcoin, we don't need to have complete knowledge about Bitcoin, we can start investing only if we know the basics.
Preliminary planning is always very important before starting a new investment. A novice should take firm decision before starting investment, he should not think about profit, his plan should always be long term. If a new investor makes a proper plan and believes in the future potential of Bitcoin and buys Bitcoin for a long period of time, then he can definitely make a profit in the future.
There is no guarantee of profits, yet at the same time, if the bitcoin investor does not use leverage and merely buys bitcoin on a regular basis, then the most that any investor into bitcoin can lose is 100%. So each person investing into bitcoin should be using money that he does not need for his expenses and realize that his bitcoin investment is not guaranteed to go up... yet if he is investing for a long time into bitcoin he can continue to learn about bitcoin and hopefully gain more and more confidence in both investing into bitcoin and also managing his bitcoin investment, which includes hopefully learning how to self-custody most of his bitcoin rather than leaving his bitcoin with third parties in the event that he might be buying bitcoin through bitcoin exchanges.
I also agree with you, there is no 100% guarantee that bitcoin will bring us profit in the future. We can only predict the future by researching past data and it may be right or wrong. But we can never be sure. Those who are experienced and well versed in crypto know very well that no one can predict Bitcoin or other currencies with 100% certainty.
But researching the past of Bitcoin shows that there is a high probability that Bitcoin will become much more valuable in the future than today and everyone believes it, so every investor is investing and holding Bitcoin as much as they can, and thus given the popularity and demand of Bitcoin are day by day increasing. As a result, there is a high probability that Bitcoin will definitely become very expensive in the future. And those who are buying DCA and "hodly", they will stand to benefit immensely in the future.