07-04-2015 08:52 PM
Probably because it is having trouble autofocusing. Either you are indoors in "dim" light, which is not always dim to the eye, or else you may be too close to the subject or the subject does not have enough contrast for the camera to grab focus. Usually it is the dim light though.
As is often the case in photography, one solution is throwing money at it. A 5D3 can autofocus at -2 EV, and a 6D can autofocus in -3EV light. The 60D cannot focus in that little light.
07-05-2015 01:10 AM
The failure to focus thing was my biggest gripe when I was using a T3i. (I also disliked the noise, grain, lack of detail at ISO above 800) Light that seemed fine to my human eye was dim to the camera. A seemingly well-lit restaurant, or a basically normal evening in a living room was "dim" to the camera. You go to take a shot, and you get this embarassing and frustrating 3 or 5 or 8 seco9nd lag, while the camera flash is madly strobing the scene, trying to get enough light to autofocus. Ug.