If you flip a coin which is known to be weighted $100$ times and it comes up heads $80$ times, then you probably have a guess as to what the weight might be.
One way to formalize this intuition is to ask "Of all the possible weights $\theta \in [0,1]$ I could have used, which value is most likely to have produced $80$ heads?"
Now, it is true that for any particular value of $\theta$ the chance of getting exactly $80$ heads is quite small! $L(\theta) = \theta^{80} \cdot (1-\theta)^{20}$ is pretty tiny no matter what value of $\theta$ you choose. However (and you should do the Calc 1 problem here!) it is maximized when $\theta = 0.8$.
How large $L(\theta)$ is in an absolute sense doesn't really matter. We really only care that $L(0.8)$ is larger than $L(0.5)$ or $L(0.6)$ in a relative sense.