With beginners, most people struggle when they first encounter bitsets. Here are two important ideas to keep in mind:
Every bit is independent.
The most significant matters more than all other bits combined. For example consider number 15. In binary, it is represented as 1111.
The most significant bit (leftmost) is 1, which represents 8. The sum of all other bits (4 + 2 + 1) is 7. Which is less than 8.