What the position obliges
A put gives its holder the right to sell 100 shares at the strike. If you sold that put, you are the party who must buy them. The premium you received is yours immediately and unconditionally; the obligation lasts until the contract expires or you close it. Nothing about that obligation depends on what you think the share is worth.
Cash-secured describes how the obligation is funded. The broker reserves the full purchase amount, strike multiplied by 100, so the cash to complete the assignment is already committed. A put struck at 45 therefore ties up 4,500 dollars for the life of the contract. That capital is not lost, but it is not available either, and its opportunity cost is the quiet expense of the position.
The three ways it ends
First, the share price stays above the strike and the contract expires worthless. The premium is kept, the collateral is released, and nothing else happens. This is the outcome the position is usually opened for.
Second, the price falls below the strike and you are assigned. 100 shares arrive in the account at the strike price, the reserved cash pays for them, and you now hold stock bought above the prevailing market. Your effective entry is the strike minus the premium received, which is why break-even sits below the strike rather than at it.
Third, you close the position early by buying back an identical put. That ends the obligation for whatever the contract now costs, which may be more or less than you received. Closing is always available while the market is open, and it is the only one of the three outcomes fully under your control.
Where break-even sits, exactly
Break-even for a written put is the strike minus the premium. Sell a 45-strike put for 2 and the position is level at 43: assigned there, you paid 45 a share but collected 2, so your net cost is 43. Below 43 the position loses, one-for-one, exactly as holding the shares from 43 would.
That last equivalence is the honest way to describe the risk. A cash-secured put has the downside of owning 100 shares from the break-even price, and the upside of a fixed premium. It is not a low-risk position; it is a fully funded one with an asymmetric payoff, and those are different claims.
The framing to avoidDescribing the premium as income invites a comparison with interest, and the comparison does not hold. Interest is paid for lending; this premium is paid for accepting a specific obligation with an unbounded-to-zero downside. The cash flow is real, and so is what was sold to obtain it.
Assignment is not a failure
If the position is assigned, the contract has done what it always said it would. The shares arrive, the reserved cash pays for them, and the broker sends a notice rather than asking a question. There is no mechanism to decline, and no partial outcome: assignment on one contract is always 100 shares.
Assignment can also arrive early, because listed US equity options are American-style. In practice early assignment on puts clusters where there is almost no extrinsic value left, which usually means deep in the money or close to expiry. A writer should assume the shares can arrive at any point, and hold the position only if that arrival would be acceptable.