Sizing without an edge
An edge is a reason to think the price is wrong in your favor. Sometimes a position has none: the numbers we can see do not show one, or they show a gap too small to trust. Plenty of people take such a position anyway, because they like the team, the company or the story. That is a choice, and it is always the reader's. This lesson is about how big that choice should be, and the short answer is smaller.
Why smaller
Size is how much a position can cost you if it goes wrong. With an edge, the odds lean your way over many positions, and a bigger size is how that lean is put to work. With no edge, nothing leans your way. The position is a coin flip with a cost attached, so a larger size adds only more to lose, with no extra reason to expect it back. The less evidence you have, the less you should lean on it. That is the whole idea behind no edge: say so plainly, and let the size say it too.
Risk is the size of a plausible move
Two positions can look alike and carry very different risk. What matters is how far the price can plausibly move against you before the question is settled. A heavy favorite priced to win most of the time can still lose, and a long shot can finish far from where it started. The market itself gives a hint. Where the options on a stock are traded, their prices imply how big a move traders expect, and a sportsbook's spread and over/under say something similar about a game. A wide expected move means a wide range of outcomes, and a wide range means the same size can cost much more.
Matching size to the move
If two positions are the same size but one is priced for a much larger move, that one is the bigger risk even though the number on the ticket is the same. Keep the risk steady, not the size, and the larger plausible move gets the smaller position. This is not a formula and it does not depend on your bankroll. It is a habit of asking "how far could this go the wrong way?" before asking "how much?"
Why it adds up
Positions with no edge do not average out in your favor. They carry the same variance as any other, plus the cost of the price, and a run of bad results is entirely ordinary. Keeping each one small means a bad stretch stays a stretch and not the end of the plan. Sizes that feel comfortable on a calm day tend to feel different after three losses in a row, so decide before, not during.
The decision is yours
None of this tells you what to do. A position the numbers do not support can be a fine thing to take for your own reasons, such as interest, a view the numbers cannot see, or just enjoying the game. What the numbers can do is show you the difference between a position with a case behind it and one without, so the size you choose matches the confidence you actually have. If you take one anyway, keep it small enough that losing it changes nothing, and be honest with yourself about which kind it was.
Example. (illustrative, not live data) Two positions with no edge shown. The first is priced to move about 2% either way before it settles; the second, about 10%. Take the same size in each and the second can plausibly cost far more, so it is the larger risk even though the stake matches. To carry a similar risk in both, the second needs a clearly smaller size than the first. Neither has a case behind it, so both sit well below the size you would use where an edge was shown. The numbers set the comparison; the choice of size, and of whether to take either, stays with you.