I had a boss once that asked a lot of me. He routinely asked me to do things that I didn't know how to do and expected me to get it done.
He gave me one task in particular that had a deadline that I quickly realized I couldn't meet. There was just too much on my plate and not enough hours in the day. I went back to break the news to him, "Hey sir, about that task you gave me earlier. I can't get it done on time because-"
"No. Fuck that!" he interrupted my expertly crafted excuse. "Listen, don't ever tell me you can't do something. Tell me what you need to get it done."
He went on to explain that I was evaluating my ability to accomplish the task solely based on myself and my own resources and limitations. He pointed out that the task could be easily accomplished if I asked that he assign another person to help me or if he pushed the deadline back by a day.
That single lesson has been foundational in shaping my view of myself and how I approach life and my parenting. It's a struggle to teach this to my sons because so many other adults in their lives allow them to say "I can't" and let them slide. Truthfully, sometimes I find myself among them.
The times when I catch myself, however, I've been able to turn what would otherwise be a frustrating failure into a teachable moment. My goal is to instill in my sons, early in their lives, the mind set of being able to look at a daunting and difficult task and not quit before they've even tried to overcome it.
The list of reasons why you can't do something is going to be long and reasonable. Don't look at that list and think to yourself, "Here's why I can't do that." Instead, think "What do I need in order to enable myself to overcome these obstacles?"