The founder of a $40 million company says this is the biggest difference between being an entrepreneur and a successful business owner

In today's startup-centric world, almost anyone can launch a business and call themselves an entrepreneur - but building a successful company isn't quite as easy.

Erin Condren, the founder of an eponymous $40 million stationery company, says there's a simple trait that divides those who manage to bring their businesses to the next level ... and those who can't.

She says entrepreneurs who end up being successful business owners are the people who are willing to make - and stick to - tough decisions, even if they're working with family and friends.

"As an entrepreneur, you usually start something with friends, family, or acquaintances who you know can help you out because you can't really afford 'real' employees at that point," she explains. "When I started, that's what I did. I come from the most wonderful family ever, but every family has dysfunction and you sort of start creating this dysfunctional family in your own business."

The ability to make tough calls and hold your ground - even when it means going head-to-head with loved ones - reveals a crucial difference between those who have the grit to run a growing business and those who don't, she says.

For Condren, this realization arose during an early conversation with her partner. "He told me, 'As we grow, it's going to be hard, there's going to be decisions that aren't easy for you, and a lot of entrepreneurs can't hack it. Can you hack it?'" she recalls. Her response: "Yes, I think I can!"

And she was right - she could.

Condren just celebrated her company's 10th anniversary and has seen sales double every year since its inception. Known for its iconic day planners, the business has inspired a thriving online community and now has products available through office supply giant Staples.

Though Condren attributes much of her success to the quality of her products, her tenacity from the start helped her turn the business from an idea into a reality.

"Many people can be entrepreneurs, but very few people can make that step from being an entrepreneur to a successful business person," she says.