There are people who are lucky. They are those who are very good at chances. They often win when they bet on something. Others get to be lucky on the first few attempts and it is followed by several successions of losses. Wanting to get back what was lost, he or she will bet again and again only to find out the the earlier winnings have been all gone plus the initial money that has been used to start the trend. Even the casin0 bonus ended lost.
There are others who bet who are not really gámblers, instead, they make use of logic and math and a lot of self control. Very few are counters. Actually if you are caught counting, you will be sent out if that was a real casin0 you entered and not merely a virtual one from the internet. The latter often offers no deposit bonus so that you can try the site for free. If you win, the winning is yours but usually you will only be able to get it if you are ready to play with real money.
Casino bonuses are there to give you the feel of the ease of playing without actually losing your own money. If you win, then you have something to look forward to, unless you become a gámbler and lose everything.