That it takes industry longer than you expected for it to move on to the next new thing.

I made this mistake in 2012 thinking that my product would no longer be wanted by 2016 and so didn't invest in expanding sales. 2017 has arrived and our sales are at an all time high and I have no idea when the market will start to decline. I lost a huge amount of money getting this wrong.

In my defence eveyone else in our industry thought the same thing and made the same mistake.