My suggestion would be to eliminate dice rolls for things that should pose absolutely no challenge to your character. An experienced thief wouldn't fail at unlocking a simple lock,.
That's taking a 10 + bonuses when not under stress. There aren't that many situation not under stress in the EA. Also, level 1 to 4 aren't what I would call experienced.
Failures aren't the result of "I don't have the strength to do that" unless you can never succeed (i.e. DC is higher than 20 + your bonuses). A very strong person can fail to lift a wood plank if they have a cramp for example. 5 minutes later they might be able to do it.
