Don't be me - a reminder to give yourself time changing train stations in Paris

I travel to Paris often and have become a bit cavelier about "getting around" the city, thinking I'm an "expert." Ha! I have been duly reminded I am NOT an expert.
We were traveling from Bordeaux to Luxembourg by train. "Easy peasy!" I thought, as we could just grab a taxi or Uber from Montparnasse to Gare de l'Est. Except....I bought tickets that only allowed 50 mins to get between train stations and, by car, it takes at minimum 45 mins mid-day. Something I did not think to check until the morning we were leaving. "No problem!" I thought. " We'll just take the Metro." Alas, the metro between the 2 stations is M4 where there are a lot of pick pockets. It is important to note, not all pick pockets are nefarious looking or run in groups. Some look rather ordinary, taking advantage of people like me who schlep luggage, back pack, coat, purse, etc. through a crowded car. I was a sitting duck.
Once we arrived at Gare de l'Est, I discovered my backpack zipper had been opened and been shuffled through. I did not feel anything but definitely knew who it was--a very average looking late 20 something white guy (the only one next to me.) Thankfully, nothing was taken as there was nothing but books, paper and dirty clothes in my bag (all of which he would be welcome to have.) But....this was a great reminder for me to check my routes more carefully BEFORE I purchase and be more mindful of my surroundings.