Is it true that our eyes shut automatically sometimes? 

Yes, it is true that our eyes can shut automatically sometimes. One common example of this is the blink reflex, which is a quick and involuntary closing of the eyelid in response to a stimulus such as a bright light, a loud noise, or a puff of air. The blink reflex helps to protect the eye from potential harm, such as dust or other particles in the air.

In addition to the blink reflex, our eyes can also shut automatically in response to other stimuli or conditions, such as fatigue, stress, or certain medications. For example, some people may experience "microsleeps" where they briefly nod off for a few seconds without realizing it, and during this time their eyes may close briefly before reopening again.

It's also worth noting that while our eyes can shut automatically in response to certain stimuli or conditions, we can also consciously control our eye movements and close our eyes voluntarily if we choose to do so.