We have all learned unexpected things through our travels, so my question is, apart from the usual advice, what wisdom have you acquired (and how)? Most of my wisdom was acquired in Italy, but I would love to hear yours.
For starters:
Get to Europe sooner rather than later. Not only an existential philosophy, but after a lifetime of cancellations, delays, and rerouting, I find it best to get from my home airport directly to somewhere in Europe, if possible. Once you are there, it's much easier to find alternate transportation to your destination city, should that be necessary. If you are stuck in the US or Canada, there may only be a few flights per day to Europe.
Put aside some emergency euro for unexpected travel expenses, such as a €50 ride between cities when a bus never shows up, or there is no public transportation on a Sunday but you did not realize that.
Monday is a good travel day, you avoid the Sunday scheduling problems and many museums, etc., are closed on Mondays, making it a good day for long distance travel.
Always trust a local to tell you where the local bus stops. They will know long before signs are posted or replaced.
Keep in mind that the bus may stop at an unsigned spot for a local because he/she is a relative/friend/colleague, or a pretty young woman. If a member of one of these categories is not waiting with you at an unsigned stop, your chances of success spiral downward.
Proof that tipping is not expected in restaurants: the waiter doesn't bring your change in small bills or in coins. That would not happen in the US.
Avoid scheduling several changes of transportation in one day. I once needed six trains and buses to get to Matera; the first train was ten minutes late and all the dominoes started falling.