In theory, it all seemed so easy. Put together smartphone parts like they were Lego blocks, and give users complete control over their phone. But that turned out to be more challenging than engineers thought, and now we know why.

After announcing its modular smartphone concept was being delayed to 2016, Project Ara revealed the main issue was due to the system’s electropermanent magnets. Ugh, how do they work?

Unlike traditional magnets, Project Ara’s electropermanent magnets used short pulses of electricity to stay magnetized, allowing the modular pieces to remain in place. It was a clever alternative, and allowed users to easily swap parts as needed. But the method wound up being a little less durable than originally thought, with the connectors failing to survive drop tests.

With electropermanent magnets no longer an option, the team said it will instead utilize a “signature experience” to attach and detach modules. No clue what they’re alluding to, but it sounds awesome.

Project Ara teased an announcement for a test-launch here in the U.S., so hopefully we’ll learn more soon.