It depends what your goal is - there are some contributions you can make at an employer on day 1. There are other contributions that demand deeper understanding

It depends what your goal is - there are some contributions you can make at an employer on day 1. There are other contributions that demand deeper understanding of more things. If you're joining the best self-driving-car company because you want to see self-driving cars halve road deaths in the United States - you're not going to achieve that in 1-2 years :)