Trust is based on experience with yourself and your partner. It is knowing where your own boundaries are and how close your partner will come to those boundaries in the different circumstances in which you are with them or in which you play or explore BDSM with them.
With a new partner you spend time observing them and how they react to you and with you. As you get more experience with them you begin to let down your guard as your confidence in their abilities and their understanding of you grows.
Hard limits and soft limits are a strategy people use to ensure their safety and to feel comfortable as they build trust in their partner before that trust is fully developed. Once you and your partner become more aware of each other's boundaries the explicit use of hard and soft limits becomes less important.
Trust is built over time:
- By consistently respecting the limits your partner has expressed, has implied, or has demonstrated,
- By being open and honest, particularly about things you don't understand and about your own mistakes,
- By demonstrating that in moments of passion or intensity your own desires or needs don't push you to overstep your partner's limits,
- By being generally consistent and predictable rather than making irrational choices or by being wildly impulsive.
Trust is easily and quickly destroyed. It can happen in seconds and in extreme cases you may not be able to build it back up.
Trust can be destroyed:
- By being selfish. I.e., by putting your own needs above the limits of your partner,
- By being manipulative or dishonest, or simply by not being open,
- By being inconsistent or unpredictable.
Trust develops when you and your partner begin to understand the range of possible ways you each react in different circumstances. It comes from both familiarity, and from having been through a wide range of situations together. When you are confident that you know in broad terms how your partner will react to different things then you can start to trust them.
Trust doesn't, however, mean that you'll necessarily be able to get along with them (or them with you). For example, if you have learned that someone responds immaturely under pressure (e.g., they run away) then you can trust that they're a bad choice for high risk BDSM activities. They might be ideal for fun and light BDSM games and knowing this helps you work out in what situations they can be trusted.
More explicitly, we're talking about positive and negative trust. When you know the situations in which you or your partner will respond well and productively then you have positive trust. When you know the situations in which you or your partner will respond badly then you have negative trust. Both types of trust are important when selecting the times someone can or cannot be involved with you, and you with them.