I think we're primed by our society and culture to make a lot of mistakes when it comes to working hard. Here are three big ones:

We mistake working long for working hard. When I was at Accenture this was rife. On projects people consistently worked 12- to 14-hour days. It was a badge of honour. At 7 pm pizzas would arrive and the project team would all take a break, then get back to work. People worked long hours, but definitely not effective hours.
We think working hard is virtuous. I'm a good person if I work hard and am not if I don't. In our minds we are either hard-working or lazy.
We equate working hard with getting results. We think that just because we’re putting in a lot of effort, that we’re doing a good job, and the results will follow.

Adopting these mistaken beliefs doesn’t fly in a practice (or in life, really). Working long, ineffective hours is obviously counterproductive. In a practice you're paid for the value you deliver ... and for your mojo, for who you are being. Not for the hours you put in.

A good alternative to hard work is what Cal Newport calls Deep Work. My friend Dermot Crowley talks about Smart Work.

If you're working too hard, have a look at which of the three mistaken beliefs is driving that. (Might be all three.) And then work really hard to change the belief and break the habit.