I’ve been lucky enough to see firsthand two ideas go from the back of a napkin to global businesses – first at Skype and now at TransferWise.

Looking back, the ideas behind both companies seem like common sense: letting the whole world speak for free and making international transfers as easy as sending emails. But in fact both were a completely new way of looking at things. A way that the incumbents in the sectors either couldn’t or wouldn’t consider. It was not legacy technology that stopped the incumbents. It was them being tied to a legacy business model. That of poor service and high fees.

Here are three lessons I learned from that experience that could help others turn great ideas into reality:

1. Know what problem you’re solving

While in two very different sectors, both Skype and TransferWise were born out of frustration. In 2003, when we launched Skype, the internet infrastructure was ready to start offering a much richer communication experience and consumers were quick to adapt. In 2011, when we launched TransferWise, it was our frustration with banks not giving us what we wanted or needed as customers. The motivation was a strong desire to solve a problem: not just fix something that was broken but create a better alternative and a new system for doing things. Big problems are overwhelming, but when we distill them down to their simplest forms, then the solutions become simple too.

2. Test the solution

The only way to find out if an idea is any good is to try it out: build it and see what happens. At both Skype and TransferWise, we were told “it’ll never work”. Is there enough bandwidth and computing power for this to work? Will people speak to their computers? These were the common questions for Skype. In the case of TransferWise, the major doubts were about trust – will people trust you with their money? Then we built the first minimum viable product. Not only did it work, but people were quick to adopt something that was cheaper (or free), faster and easier to use. From then, it’s an ongoing process of development, testing, improving. Rinse and repeat.

3. Keep crossing boundaries

Keep asking “what if…?” An idea comes from going beyond the usual confines of our thoughts and crossing those boundaries. Steven Johnson talks about “one door leading to another door”: the adjacent possible. There’s no single Eureka moment but a series of opportunities and possibilities that leads you to a new alternative. A good idea takes on a life of its own and finds those doors. That’s the excitement of innovation.

A seed depends on a whole host of factors to grow – from the fertility of the soil to the right mix of rain and sun, to not being eaten by a passing bird. The same goes for an idea. For an idea to really take hold, other factors come into play, from timing to the emerging technology that makes it possible. In fintech, it is the perfect storm of a loss of trust in the banks, the rise of mobile and the experience of better in other sectors that means consumers are willing and ready to embrace non-bank alternatives.

But you can only reap what you sow. The most important thing is to just get on and plant the seed.