If the ground has never been tilled or its been a lont time or if critters have been stomping on it for a long time,, it's going to be hard packed, also the kind of dirt is a factor as well also WHEN he is tryig to till,,, hot dry ground caked hard not a good time to till, clay, rocks tree roots, also if its not been tilled before the take it in layers, like 2 or 3 inches at a time,, I have seen folks just sump the tillers in and cant figure why they dont work like they think they should. Sharp tines help too and make sure they are in the right direction to CUT the dirt, if you turn them around they work well for turning up the soil for mixing in manure and stuff, AFTER the soil has been worked reallllly good. Hope some thing here helps
Peace
Skeets