So to first quote Hsu's description:

This graph displays the number of GWAS hits versus sample size for height, BMI, etc. Once the minimal sample size to discover the alleles of largest impact (large MAF, large effect size) is exceeded, one generally expects a steady accumulation of new hits at lower MAF / effect size. I expect the same sort of progress for g. (MAF = Minor Allele Frequency. Variants that are common in the population are easier to detect than rare variants.)

We can’t predict the sample size required to obtain most of the additive variance f