Stanley - I'll try to answer your question but this just my "educated guess". Look at the daily chart for MA - it shot up from 242 to almost 300 in a few days in end of April. Then it was resting for a while and the price pulled back mostly on lower volume to around 275. At that point, investors found support and started buying in. As the price started to go up, more investors got in and finally you got the big pop y'day. It broke above 300 which is a pyschological barrier so I am hoping it will continue soaring. Visa went up (I think) because of MA's price action. Many investors won't buy MA because of its high price and will instead purchase V. But I expect MA and V to be traded in tandem.
Don't beat yourself up too much - stocks usually retreat after a big pop. So keep looking for buying opportunities.