There is a degree of trust required in your chosen validator(s). As stakers, we are delegating our stake to these validators to act in the best interests of the network, in exchange for emission rewards.
However currently (at the time of writing) slashing has not yet been implemented on Radix, which is the mechanism in which validators (and stakers to a degree) are penalised if a validator acts maliciously (such as attempting a double spend). You can find out more about slashing here: Slashing
Aside from malicious validator activity (which is really the worst case scenario and hopefully a very rare occurence!) there are other ways in which we may need to trust validators.
For example, we need to trust our validators to operate in not only the network’s best interests, but also our own. This means operating reliable nodes with consistently high uptime.
Every validator will experience downtime at some point, due to unplanned maintenance, attacks etc… but the important thing to remember in these cases, is that your staked XRD never actually leave your wallet. In the event that a validator did go offline (or even disappear altogether) there is no risk of funds being lost. You would simply need to unstake, and after the Unstaking Delay would have full access to your XRD once again.