def most_frequent_set(lst):
    items = set(lst)
    best = [-1, -1]
    for item in items:
        occurrence = lst.count(len(items))
        if occurrence > best[1]:
            best = [item, occurrence]
    return best


print(most_frequent_set([1, 1, 5, 7, 8, 3, 8, 1, 8, 9, 1]))
print(most_frequent_set([9, 0, 4, 1, 7, 0, 2, 0, 4, 9, 1, 5, 7, 4, 9, 9, 7, 9, 2, 5]))