1. People have prepared in advance
There are many places where shoppers can go online to find ads before Friday. Retailers deliberately leak their ads to get more people in the door for the holiday. Retailers love the long lines because that means more foot traffic and more money spent. Even if you don't have the store's ad in front of you, all of the big box retailers typically have one in store by the time you arrive.
2. Pre Sales
Retailers like Best Buy, Amazon, Walmart etc. run pre-sales in advance of the first day to give consumers a taste of what to expect. These pre-sales serve as bait for the main event, giving people a small sample of the deals that they can come to expect. Pre sales can often be as lucrative as the actual sales on Friday.

3. More Likely To Run Out
Products are much more likely to run out on the day after Thanksgiving. Retail stores can only carry a set amount of inventory, so hot items tend to sell out in a few minutes. People have even been known to fight over the items that are in the most demand. Televisions seem to be the most popular items that sell out the fastest as the best deals can be found then.
4. Cyber Monday Has Best Deals on Fashion
If you're purchasing fashion items, your best bet is waiting to buy online on Monday. That's when shoes and clothes tend to be heavily discounted, and you also get to take advantage of the convenience of shopping from home instead of dealing with crowds of people. If you know your sizes, then it's best to skip the crowds and buy your favorite items on Monday morning instead.