Computer random number generators are not actually random, and its pretty common to see clustered results.
If you were to do the 60% chance say ~200 times you'd end up with close to 60% successes, just that you'd had more strings of multiple fails / successes in a row than you would get on average if it was actually random.
If you were to do the 60% chance say ~200 times you'd end up with close to 60% successes, just that you'd had more strings of multiple fails / successes in a row than you would get on average if it was actually random.