I had a transition last weekend that was so abrupt that I lost my momentum before I could get to the end of my range and fell over. I got on the granny first and was trying to grind it out while moving up the cassette. Momentum stopped and I couldn't get a foot down fast enough. Got up, shifted the rest of the way to the end of the cassette, rolled down to the start, and went back up. Luckily, there were no other riders/bystanders to witness the fiasco.
Also slowly passed a teen walking up a hill with a skateboard. Looked down and I was climbing at 4.1mph. Slow enough that we had a conversation.