The probabilistic method is a technique for proving the existence of an object with certain properties by showing that a random object chosen from an appropriate probability distribution has the desired properties with positive probability. For example: https://cpb-us-east-1-juc1ugur1qwqqqo4.stackpathdns.com/sites.psu.edu/dist/f/7257/files/2013/10/The-Probabilistic-Method.pdf
If $\binom nk \cdot 2^{1-\binom k2}<1$, then $R(k,k)>n$. Thus $R(k,k)>\lfloor 2^{k/2}\rfloor$ for each $k\ge3$.
Is there any example for getting some properties on planar graphs using the probabilistic method? We know that discharging can get many useful local structures. I feel that the probability method is also a way of counting skill.