Bikes are built for speed, just like a startup. Now and then I hear people going on crusades for adding features and business lines.
From most angles, adding a 3rd wheel makes sense: more stability, novelty and differentiation, not extremely expensive.
This has some practical business benefits: more people can use it, it's easy to market ("the bike which doesn't let you fall"), and you can increase price!
But it it's not a bike most people want. It's not what they need. A bike is a great exercise of focus in providing fast, affordable, personal transportation.
The temptation is always there to over-feature a startup's product, but there are problems which don't deserve a solution. It's critical to infer the product-market fit, but if you go around explicitly asking for customers what they want and to list problems with your product, you may end-up solving the wrong problems.
I personally always refer to the vision. Does this feature move us closer to the vision or is it a nice to have? More frequently than not, the answer is No.