Anecdote: Semester 2 of year 11, I did a SAC that was an application of calculus for Methods. After the sac I pretty much knew I failed cause I just did not know what to do. 2 weeks later I opened my result and I was hit with a 26%. For a while I had this feeling of disconsolate (very hard to describe, but the feeling wasn't pleasant), but I didn't really care too much because my teacher didn't really do anything if you failed. Well, a week later my dad came up to me and said that my teacher emailed him stating that I was at a risk of being kicked out of Methods and receiving an N for the unit, I also had to have an appointment with my teacher with BOTH my parents along... If you are wondering, yes I was very very embarrassed.
After this, I studied my absolute ass off promising to score better next time, which eventually payed off as I got 98%.
My personal advice that works for me is to really find an incentive to do better, if reflecting from a bad mark isn't enough for you, then find something else - an example, someone like my grandpa when he was the same age as me was doing things way more strenuous than me just to scrape by life, and here I was procrastinating and living life. Please take note of what other people have said, they have offered great advises.