Unless you've personally memorized all the data in your head, you're trusting someone or something. Even if you've printed it all out on acid-free paper and stored it in a bank vault, you're trusting the bank, you're trusting your paper supplier, you're trusting the courier who transports it back and forth. If you've stored it on "your" servers you're still trusting your hard drive manufacturer, your RAID firmware, your OS code, your hosting company, your sysadmins.

For most values of "I have x hours and y dollars to safely store z gigabytes", a pure-cloud solution (possibly involving multiple independent cloud providers) has a lower chance of failure than one involving local storage.