Imagine the scene: I've just completed some of my personal training session and my personal trainer says we're moving onto the above exercise (ish). An exercise I've done before lifting 20 kgs. I take the bar in hand and get ready to start. I notice it feels heavier than normal (but it isn't) and already hear my internal dialogue telling me I can't do it. I change the dialogue and do the exercise easily.
But here's what I learnt. At the time just before I started the exercise I wasn't accessing any of the resources (in this case muscles) needed to complete the task. It was only in making the first move to start that those resources turned on.
Isn't that also true in life. We can talk ourselves into not being able to do something and yet that's based from a position of inactivity. As soon as we start to look for the solution we'll certainly then engage the resources we have to make it a reality.