(This comic is a "timeline" of algorithm complexity, ordered from least to most complex. The first five are roughly equally spaced, with the last item at the extreme end of the axis.)
Algorithms by complexity
Google search backend
Sprawling Excel spreadsheet built up over 20 years by a church group in Nebraska to coordinate their scheduling
The laws of physics are fun to try to understand, but as an organism with incredibly delicate eyes who evolved in a world full of sharp objects, I have an awful lot of trust in biology's calibration of my flinch reflex.