Many traditional cloud storage providers like to pretend they offer customer privacy by saying something like, "We encrypt your data at rest in the cloud." But they're being less than honest with you because they're withholding a critical detail: They hold the encryption keys themselves.
This is the equivalent of a locksmith telling you that you're safe in your home, now that he's installed locks on your doors. But, oh by the way, the locksmith is keeping a copy of your key.
Thus, in reality, if a cloud storage provider holds the keys to your data, then they could access your data anytime they like. Or a hacker could end up getting access to your data. Or a corrupt government could demand access to everyone's data for "national security".
We set out from the beginning to do things differently. All data you store in the cloud is first encrypted on your device, before being uploaded to the cloud. And only you hold the keys to decrypt the content. Which means that the data you store in the cloud cannot be decrypted by us, or by hackers or any other nefarious organization. Only your devices (and anybody you explicitly share with) will be able to decrypt your files.