Some people are tempted to check their stock portfolio every five minutes. Others don't want to look at it ever. Should you check it and, if so, how often? I think the Talmud has some relevant advice (Chullin 105a):
Shmuel said: About this, I am like vinegar the son of wine compared to my father. My father would inspect his fields twice a day but I only inspect mine once a day. Shmuel is consistent with his opinion because he said: He who checks on his property once a day will find a silver coin (i.e. will profit).
Click here to read moreAccording to Shmuel, you need to check on your fields at least once a day, preferably twice. This is true even if you have professionals working the fields and overseeing them. Rashi (ad loc., sv. sayer, mishkakh) explains that you have to check on your fields to see if there is anything you can fix. As the subsequent story in the passage makes clear, your overseers might not be paying sufficient attention to the work or might even be stealing from you. That is why you need to personally inspect the fields at least once a day.
The Maharshal (Yam Shel Shlomo, Chullin ch. 8 no. 9) explains that this is important because you have to be careful to retain your wealth. If you become poor, the community will have to support you and you have no right to bring yourself to such a situation. Therefore, you must check on your fields and make sure that you do not lose substantial amounts of money. The Iyun Ya'akov (on Ein Ya'akov, ad loc.) goes so far as to state that there is a prohibition to ignore your fields.
How does this relate to your portfolio? Even if you are not an active trader, if you have the ability to reallocate within your portfolio (even your 401K) then you have assets that need to be watched like a field. You might have a financial adviser but overseers also need to be watched. Therefore, it seems that this talmudic advice would be translated into making sure to check your portfolio once a day, twice being even better. It could be that you will not find anything you can do, maybe for years. But all those days of checking will be worthwhile the one time that you find something.
Many people have no problem checking their portfolios every day and actually check them obsessively all day. On that issue, listen to this lecture by R. Mayer Twersky: link.