The 'proportional theory' suggests that each unit of time (like a year) feels shorter because it represents a smaller fraction of our total lived experience as we get older.

Imagine you're five years old. A single year is a huge 20% of your entire life so far! It feels incredibly long, packed with growth and new discoveries. Now, imagine you're fifty. That same year is suddenly a tiny 2% of your life. It's easy to see how a year that was once a huge part of your existence now feels like a tiny blip. This simple math makes a big difference in how we sense time passing.