Odd MySQL Database Corruption

Today I checked the MySQL backups for ziggy and noticed that the database hadn’t been backed up properly in weeks. I manually ran the backup script and was greeted with the following error:

Table 'mytable' is marked as crashed and last 
(automatic?) repair failed

To correct this, I opened a MySQL console and repaired the table with:

REPAIR mytable;

This appeared to correct the issue, but like most computer problems, I have no idea why it happened in the first place.