Investing is buying an asset assuming that you will be able to sell it more expensively in the future.
Lets really think about this. In other words, every time you make an investment, you are explicitly saying “somebody will be willing to pay more than I did for this”. Implicitly, you stating “there exists a greater fool that me at some point at a time greater than now.” That is a powerful thought.
Anytime you buy an asset someone is willing to sell it to you. Anytime you sell an asset somebody is willing to buy it. When the price goes up, that means more people demand it. When the price goes down, more people are selling.
What should be going your head now is what is going through their (the person on the opposite end of the trade) head? Why is someone willing to sell me this asset that I "know" will appreciate or buy this asset that I "know" will depreciate?
All money in the market is redistributed from someone else. More concisely, somebody is betting against you, always. Keep this in mind before you are tempted to think about market movements in absolutes. Nobody knows for sure which way the market will move. Be humble