求翻译：15. 汤姆过去一向认为，他在学习上花的时间越多，就会取得越好的成绩，但现在他已经认识到，情况并非都是如此是什么意思？

15. Tom has always held that in the past, he spent more time in learning, you will achieve better results, but now he has realized that this is not always the case