9. Not walking or biking everywhere you can
Cars are a pain in the butt in central Amsterdam and best saved for trips beyond, and public transport usually takes longer than the bike ride, with all that stopping and waiting around.
10. Not having a smartphone
In this twisted-street town of watery dead ends, even longtime locals depend on Google Maps.
11. Trying new drugs without proper guidance and supervision
Even "soft" drugs like truffles and cannabis can hit you harder than you expect, so do pay attention when the instructions are doled out if you're going to try 'em for the first time. And then only do it somewhere safe with trusted people looking over you (and standing by with a fruit smoothie when needed).