[jhanschoo]

You're adopting the micro perspective to a macro problem of a finite supply of coins.

Finite supply means that on average, net coin-profit of a business is zero coins. With such poor odds, why should someone go into business? Inflation incentivizes investment since you know that on average, a business opportunity has better ROI than saving.

[dpc_pw]

If you can produce 3BTC worth of goods using 2BTC, then people will pay you 3BTC.

Your doubts are based on the assumption, that somehow "there would be not enough money", which is simply not true. During the process of producing and trading goods money are not destroyed. They are just changing hands. There is always enough money in the economy.