Missing the timing is the inability to activate a card or optional effect when it would meet its activation timing because it is not possible to activate it in response to the required event.
Cards and effects can only be activated in response to an event if that event is the last event to occur. If an event is performed, then before it is possible to activate cards or effects another event is performed, it is not possible for any cards or effects to be activated in response to the initial event.

Some Trap Cards, Quick-Play Spell Cards, and optional effects must be activated in response to a particular event (such as the Trigger Effect of "Peten the Dark Clown"). These optional effects are marked by the usage of the word "when" in their activation timing. Trap Cards, Quick-Play Spell Cards, and optional effects that use other words instead of "when" (such as "if" or "each time") do not need to be activated in response to the event, but simply at the first opportunity after the event occurs. Likewise, mandatory effects do not need to be activated in response to a particular event, always being activated at the first opportunity after the event occurs (regardless of whether they use "when" or not).

If a card or effect is activated in response to an event, all cards and effects activated in the same Chain are in response to that same event. For example, if a monster declares an attack and a player activated "Magic Cylinder", then "Mirror Force" can still be activated as Chain Link 2 or higher because all cards activated in this Chain are in response to the attack.

Chain Links resolve strictly sequentially. The last Chain Link to resolve will be the most recent event (and the only event that can be responded to). Normally this will be Chain Link 1, but if the activation of a Chain Link is negated, it does not resolve. (There is a distinction between negating the activation of an effect and negating the effect itself; if only the effect is negated, the Chain Link still resolves, but without effect.)

It is not possible to activate cards or effects in response to events that occur as part of paying a cost to activate a card or effect.

Simultaneous events
When resolving a card effect, different parts of an effect may or may not be considered to be performed at the same time. As such it is possible for there to be multiple most recent events.

Cards with Problem-Solving Card Text have mechanically significant conjunctives ("and", "and if you do", "also", "then", "also, after that") in their card text which determine whether or not different parts of an effect are considered to be simultaneous. In the TCG, for cards without Problem-Solving Card Text, it is necessary to rely on rulings for details on simultaneity.

The conjunctives "then" and "also, after that" indicate that the part of the effect before the conjunctive is done strictly before the part of the effect after the conjunctive. Therefore, if the part of the effect after the conjunctive is applied, cards and effects cannot be activated in response to the part of the effect before the conjunctive, and so effects that could be activated in response to that event miss the timing.

On the other hand, the conjunctives "and", "and if you do" and "also" indicate that both the part of the effect before the conjunctive and the part of the effect after the conjunctive are done simultaneously. Therefore, if the part of the effect after the conjunctive is the last part of the effect to resolve, cards and effects can be activated in response to the part of the effect before the conjunctive (so do not miss the timing).