This rule is not about being honest with others, it's about being honest with yourself. Many students lose hope and confidence so easily when it comes to doing maths. The "I'm not mathematically minded" or "I'm not smart enough to do maths" comments are everywhere.
The reality is, most people lose hope long before they've given maths a real shot. Remember: "you are not asked to do something beyond your reach, you are asked to do your best, and that is within your reach"
Could you, in your most honest state, look within yourself and say that you have given mathematics your best and you still failed? Most likely the answer is no…. Now trying to do a question for 10 mins, getting frustrated and stopping your studying all-together is not your best. Spending an hour on a topic and then giving up because you don't understand it, is not your best. Remember the "get another textbook rule"? Always apply it.
The most important thing is to always be honest with yourself and really monitor whether you are doing your best or not. One way to ensure you're studying enough is to follow my guide on studying effectively