Investing $100? I don't see any profit from it actually, we can never expect that amount it grows into $150 or $200 and this is the reason why. I am supposed to say to make use of this amount to explore the market, adding more funds could be next if we are sure that we can handle the stress already.
Back in 2020, $100 in March 2020 could buy 0.02 btc then. In March 2021, $100 will be $1,200, and in March 2022 $100 will be $800. Then how can you not imagine the potential profits that could be made in the years to come with that $100 if bitcoin hit ATH again or went up to $40K or $50K?
People don't have to be too greedy about investing, they just do it for whatever they can afford to lose. $100 could become $200 if the bitcoin price doubled from now and that is a possibility that can still be believed to be achieved this year and years to come.