One Direction are going full-speed ahead -- and it has Simon Cowell worrying about them.

The guys have been working pretty much non-stop for the past few years -- and particularly within the past few months, releasing their fourth studio album mere weeks after concluding their worldwide Where We Are tour. And of course, with 'Four' comes even more promo and another worldwide tour in 2015, aptly named the On the Road Again tour. We're exhausted just thinking about it!

"They can't carry on doing the amount of stuff they've been doing for long because they'll burn out -- it's a high-class problem," Simon told the Sun (quote via Sugarscape). "But they don't complain about working hard." In fact, they pretty much seem to enjoy it.

In a recent interview, the guys tease their upcoming 'New Year's Rockin' Eve' performance and reveal why the holiday is so important to them. (Psst: it's because they're psyched about the future, obvs.)

"You can reminisce on the year and look onwards," Liam explained about their love for New Year's, literally looking, well, onwards. "Into the future. Happiness. What's around the corner?"

He went on to add that the band will be performing "a host of older songs" on NYE, as well as some newer tracks as well. Specifically, the guys will be singing 'What Makes You Beautiful,' 'Story of My Life,' 'Night Changes,' and 'Steal My Girl.' Eek! You can watch them reveal this in the video below.

While the guys are basically running around like five Energizer bunnies right now, the big boss ultimately has faith in the longevity of their career.

"They're going to be around as long as they want to be, because they're talented and good writers -- and they understand their fans," Simon explained.

YAS. 1D forevs.

Swoon City! See One Direction Throughout the Years

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