In this segment from the MarketFoolery podcast, host Chris Hill, Million Dollar Portfolio's Jason Moser, and Stock Advisor Canada's Taylor Muckerman each give their answers to a query from a listener who makes changes to his portfolio so rarely that he doesn't have any ready candidates to replace a stock he now wants to sell. The right number of stocks to own is a much-discussed concern. But today's question is less common: How many should you be holding in reserve?

A full transcript follows the video.

This video was recorded on Feb. 26, 2018.

Chris Hill: From John Lombard in New York. John writers, "I'm a very long-term investor. I almost never have occasion to sell, so I was caught off-guard over the weekend when one of my investments no longer seemed to fit into my investing thesis. I realized that I don't really have much of a backup list, or a watch list, if you will. I focus a lot on the stocks I already own, but since I almost never sell, I've never given much thought to what I would replace one with, should it go sideways. I know people ask constantly about what the right number of stocks to own is, but I'm wondering, how many stocks do you guys typically keep waiting in the wings? Thanks, and I hope you can come back to New York City soon." I do, too. That was a great trip that we took up to New York. I'll just speak for myself. Taylor, not many. My waiting list is usually single digits, and it's usually low single-digits, just because I don't make that many transactions, so at any given time, I'll have maybe three to five stocks that I have on a watch list. What about you?

Taylor Muckerman: I don't know. I think mine right now is probably anywhere from 15 to 20. But half of those probably aren't really serious, they're just companies I'm interested in, and maybe one day down the road they strike my fancy enough to join the portfolio. But, probably the core watch list is 10 or so.

Jason Moser: Yeah, looking through the Million Dollar Portfolio, the way we're running things there, we have a portfolio with 34 holdings today. Now, one of those is a dual-class with Google, or Alphabet, so we actually have 33 companies in there. We have a watch list with 32 ideas. Now, we also have three analysts on the team.

Hill: I was going to say, you're on a team.

Moser: So, break that up, and maybe you have 10 to 11 names per analyst that we're covering and watching. And I would say that's on the high side. My personal watch list, I think, is around six businesses right now that I don't currently own. But the point that he alluded to there earlier, I think, was that a lot of times, the best idea is a stock you already own, and adding a little bit to a position in a stock that you already own. I know that I look at my portfolio often, and rather than looking at my watch list, I'm looking at some of those companies that I've held for long periods of time. I've gotten to know them better, they're good performers. You like adding to businesses that are winning. So, often times, really, the best idea is when you already own. But, I think keeping a watch list with something like five names seems manageable.

Muckerman: And sometimes I'll even throw a company I do own on my watch list. If you hold it for a couple of years, your return is going to be different than, maybe, if you started watching it six months ago. That way, you can see different fluctuations in the stock price. And maybe in your portfolio, if you've had a long run, a 10% move down isn't going to be a noticeable reflection there. But if you just added it to your watch list and all of the sudden it's down 10%, you're like, "Oh, maybe I should take a closer look to add to this position."

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Chris Hill has no position in any of the stocks mentioned. Jason Moser has no position in any of the stocks mentioned. Taylor Muckerman owns shares of Alphabet (C shares). The Motley Fool owns shares of and recommends Alphabet (A shares) and Alphabet (C shares). The Motley Fool has a disclosure policy.