You should first realize that the ATH (top value) is not the "normal" value. It's a peak value. When you're driving a car that can go 250 km/h you don't run it close to that speed on a daily basis. Your normal cruising speed will be somewhere in the middle or even below that. It's the same with BTC. It has reached $20k but it's normal price is somewhere around $10k. Right now we're below that, which means it's a good time to buy, but don't expect it to be at 20k in a month or 2.