Why is it unreliable to use a line of best fit far outside the range of the data?

The pattern may not continue, so it is extrapolation

AQA GCSE Mathematics Statistics overview quiz quiz

12questions. Pick an answer and you'll see why right away.

Which of these is an example of continuous data?
What is the mean of the values $4, 6, 8, 10, 12$ ?
What is the median of the values $7, 2, 9, 4, 6, 1$ ?
Scores of $1$ , $2$ and $3$ occur with frequencies $5$ , $2$ and $3$ . What is the mean score?
On a pie chart of $80$ people, $20$ chose football. What angle represents football?
A school of $1000$ students has $400$ in Year 11. In a stratified sample of $50$ , how many Year 11 students should be chosen?
On a scatter graph, study time rises as exam score rises. What type of correlation is this?
On a histogram with unequal class widths, what represents the frequency of a class?
Why is it unreliable to use a line of best fit far outside the range of the data?
What is the range of the values $12, 7, 20, 15$ ?
Which sampling approach is most likely to give a biased, unrepresentative result?
Which value is most affected by a single very large outlier in a data set?