It's a combination of both skill and luck. You can improve your chances of winning/making a profit through skills and experience but at the end of the day you still need some luck to win certain bets. I've had lots of instances where I only needed 1 goal/corner/yellow card to win my bet with just a couple minutes of the game remaining. Sometimes it hits,other times it loses, but I personally consider it luck since it's not in my control anymore and anything can happen.