It is because we are slaves of our habits.

If your spending is low and your approach is always frugal you will never be spending more than you need but this mindset needs to be build in either by the parents mostly or sometimes the child during growing years learns this if they are intelligent enough.

Cutting down on habits that drain out your pocket is important to save money in later life once you recognize them. Use the public transport, get some steps in the walk to and fro and avoid using the car for short trips.