I've seen two companies with mid-seven figures funding, one of which I co-founded, fail first-hand. Neither of these companies validated the idea prior to building it. Based on these two experiences I'm a huge proponent of validating first, building second.

I think there are two common pitfalls that people with an idea fall into, when they choose to build first, validate second -

1 - If I think it's a great idea, there must be a lot of other people who do too.

I think this pitfall is caused mainly by the optimism that is naturally inherent in entrepreneurs. I personally have no shortage of ideas, most of which I believe are good ones :)

I took a course by Noah Kagan of AppSumo, where he suggests finding three paying customers, prior to building a product. When I started validating my ideas this way, prior to launching, I was surprised at how quickly I learned the lesson that just because I thought an idea was a great one, that didn't mean anyone else did.

2 - Building is more fun/satisfying than validating

When we're building something, we experience tangible progress and feel like we're exerting some degree of control over our future. Both of these experiences work powerfully on our conscious and sub-conscious mind.

As a result, it's easy to get pulled into a project, get enticed and distracted by the momentum that seems to building as we're making "progress", only to release the product to the market and have it fall flat due to lack of demand.

So, if it isn't clear by this point, my strong suggestion is to validate first, build second :) I think the good news is that the availability of crowdfunding platforms, landing page builders, etc., makes this approach easier than ever before.

You may also be surprised at how much work goes into validating your project, so you may still experience the satisfaction of feeling like you're making progress, if your idea begins to gain traction and/or you begin to interact and communicate with potential customers.

Good luck and always happy to discuss further on a call!