Can you really be sure you will profit unless you have insider info?
Not at all. Trading with bitcoin requires you to follow the price flow, current events that might change the price and also a little luck.
Sometimes guesing yes but you need analysis to gues. I Agree that you should follow current flow. Event and issues. The price of crypto change every minute. For a new trader, Most of my guess is wrong but now after a little time analysing curent flow I can minimize the mistake. When I should buy and when I should sell. Sometimes I let for one day not do transaction untill I got the fixed price to sell or to buy. Guessing yes but not blind guessing.