Confusion about Conditions

I recently started reading this book called Lies Women Believe. It was recommended to me by several Christian women. Basically it goes through different thoughts women have, identifies the lie at the root of the thought, then gives you Gospel truth to replace the lie. Over all it seems to be fairly solid Biblical truth, like you could see how these statements could be lies and how the truth from the Bible is used correctly. However, there is one condition put on a Biblical truth that I am puzzled by. The author is talking about the lie that "I just can't take anymore". It brings up the verse that "His grace is sufficient for me", that we can do all things "through Christ who strengthens me". Which I believe fairly solidly refutes the lie. However they add the conditional statement "this is assuming, of course, that I haven't taken on myself responsibilities He never intended me to carry. If the burden is God given, I can go on by His grace." So this raises the interesting rabbit trail of free will. God plans our lives in advance, so He knows the route we will take...does that mean everything is in His will? Or, is is slightly more basic than that. Hypothetically you decide that you want to move to Texas and raise fainting goats, or more to the Himalayas and become a missionary...you pray about if for a while and you decide that God and the wisdom of Proverbs is telling you not to go. However, let's say that you either learn this truth after you've gone to Texas or the Himalayas, or that you decide to go anyway...so you are either making a decision and then later learning that you shouldn't have, or you are ignoring the wisdom and advice you're getting. Now, according to this conditional statement, God is not necessarily going to give you strength in the trials you get yourself into outside of His perfect plan for your life. Or, does He turn all things to His will, so despite the fact that you acted out of His will to get into a situation, He will still use it to His glory...thoughts anyone? Does anyone know of any verses to either support or refute the condition?