Indeed, it is on pure luck. Sometimes, a single spin can land to a bonus round, and sometimes even with 200 or more spin can't land you a single bonus round. I had experienced them both. And what funny is even if we are lucky enough to get a bonus round, we are still unsure whether that bonus round can give us a multiplier. There are times that I won't hit a single win in a bonus round after hundreds of spin to get into it.

In the beginning when I played slots, most of the time I only played 5-6 times on 1 slot and never really won anything. Nowadays, I manage to reach bonus rounds quite easily sometimes (in less than 20 spins) but I have not received a very high multiplier. My biggest multiplier was x100 on Pirates Plenty

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But I agree, slots are fun to play but if you don't pay attention, your bankroll goes down quickly.