The teams which are playing to go to the pk shootout are usually the weakest in terms of technical skills, offense, coaching, but they do have a great cardio.
They feel they have a stronger chance to beat the favorite during a pk shootout because they face less pressure. It's a mental game, their only purpose is to make you fail in order to get into your head making you losing your temper or This.
I've witnessed so many great ones missing pks in OT or during regulation, Zico, Platini, Ronaldo, Messi in OT during the final of Copa America, Maradona missing 5 in a row in the argentinian league, etc...