If banks like Citigroup, Bank of America and JP Morgan were boyfriends, they'd be the one you can't quite trust, the one that doesn't listen to you, and the one that isn't there when you most needed them. They would be the ones your parents hate. Monzo, a new British bank, would treat you as an equal, buy your mom flowers, and always give you a call before you fell asleep.

Tom Blomfield, Jonas Huckestein, Jason Bates, Gary Dolman and Paul Rippon founded Monzo just over two years ago. Now, it has almost 400,000 British customers with a very long waiting list (as a point of comparison, Santander was losing 60,000 British customers every three months in 2015, according to the Payments Council).

More than $640 million has been spent by Monzo users. It's an incredibly popular bank amongst Millennials. At 120-strong, it's seen as nimble and constantly evolving--a stark contrast to the older, heftier, traditional banks with operational systems that act as a sort of chewing gum that stops them innovating.

Houseless and avocado-toast-loving Millennials are anxious about their finances, and Monzo seems to be providing them with a bank they can trust and control over their budgets. Entrepreneurs can learn a lot from this British bank.

What are the 'nice guy' traits of Monzo?

I had a lovely conversation with Tristan Thomas, Monzo's head of marketing and community, about the bank's services. If you have a problem with your card, you can message Monzo via an app, and a real person responds (as opposed to a bot or a call center in India). The bank also has an online forum, open to everyone and comprised of 15,000 "Monzonaughts" who discuss anything from Monzo to mimosas.

During Monzo's first four months of operations in 2015, people had to queue at the Monzo office to get their hands on a card. This way, the team was able to their first 3,000 customers individually. (They also hadn't built the facility to send them out.) Even now, Monzo still tries to create a community: It runs one or two tech-based events a week in their offices in London so they can meet their customer base.

Monzo listened to its customers from day one. So did Uber, by the way. It's a common trait among plenty of successful startups.

The long-term vision is important.

In the long term, Monzo aims to be the financial control center of your life. In the short term, it's currently running at a loss.

The bank wants to be able to estimate how much someone your age and location should be spending on gas; then recommend a cheaper alternative, with energy firms, as one example, paying to use the platform.

Amazon and FedEx ran at losses in their first five years, too. The three things they all have in common? A future business plan with great value.

Focused vision and a bit of wishful thinking are vital for any entrepreneur. Dream big.

A technical advantage is important, too.

As Thomas told me:

"I don't think I can understate just how far behind these banks are when it comes to technology. They have to un-retire people in order to get maintenance done on some of the systems because only the person who wrote it understands the language it was written in. Ultimately they don't provide a good product, and they can't move fast enough. They're driven by these motives of offering a current account for free and then up-selling you on all these other products you don't need."

The message is that the number one priority is the customer. Keep it fresh, and don't get complacent. That's another lesson every entrepreneur should learn.