Spotkick howler still weighing on Man Utd's Van Persie
Van Persie still managed to net a matchwinning hat-trick at St Mary's.
"A career won't be always a bed of roses. You have disappointments," he said.
"Look at my missed penalty kick against Southampton last Sunday. That is what you call a disappointment.
"Taking a penalty kick in that way when you are 2-1 behind. That's just bad.
"I couldn't explain it, not even to myself. And what you do next? Do you stay disappointed? Or are you going to hunt, and get over it?
"In the game I put it behind me, thankfully. Many people can get swept up after something like that. It's happened to me (before) and it's all over then.
"Someone who is 18 years old wouldn't score two times after it. I wouldn't have done a couple of years ago.
"You have to be lucky, but you also have to force it."