The answer depends on whether you wanted to attend the wedding in the first place. If you wanted to attend and were not invited, you likely have some hurt feelings to sort out. If you were invited late, you have to scramble to take time off of work, find a babysitter if applicable, book a hotel and possibly an expensive plane ticket, etc. However, the question a late invite truly begs is “What do the bride and groom think of me?”
Rather than pondering this question deep into the night or worse–asking the bride and groom why you were not invited until now, attend if you want to and have fun. A last-minute invite does not necessarily mean the bride and groom think less of you–it could simply mean the logistics of wedding planning got in the way. Finalizing the guest list is easily one of the most challenging aspects of wedding planning when you consider input from family members, food and drink costs, etc. So forget stressing yourself–and possible the bride and groom–out, and enjoy the festivities! Weddings are always a good time, so get gussied up, drink the free booze, eat the free food, and dance the night away. You will be glad you did!