I've managed staff through a PIP. It should never come as a shock - a PIP is supposed to be a supportive and collaborative process, not a sword of damocles to hold over your head.
Yes, there is the stress of knowing that if it doesn't work out then your employment may be terminated, but done properly it should be a very clear and structured process which gives all parties time to review and decide appropriate action.
PIPs in my organisation run for a minimum of 3 months and a maximum of 6. You meet weekly with the employee to have an enhanced 1-2-1 and review their workflow and discuss how they are feeling. You have a monthly formal review and the outputs of this are used to update the PIP. The intention is that if the employee isn't managing then it will become obvious as the process continues, which gives them an opportunity to think about what to do. It should never be a set of orders to jump through hoops and then an arbitrary decision at the end.
Out of all the staff I've managed through PIPs most of them have improved and found the extra time and guidance helpful. Some have realised the job is not for them and we have identified strengths which have meant they could be redeployed into other vacancies in the firm. Others have decided that the job isn't right and that they want to leave but it's given them time to think about things and search for another job before leaving on their own terms. There's only one that I have had to dismiss, so it's very rare.
Don't panic. Make sure your PIP targets are clear, fair, achievable and time-specific (i.e. they have dates to be achieved). If there is anything you are unclear on then raise it and make sure the instructions are documented in writing (e.g. attach copies of emails to the PIP). Make sure you are having regular assessment meetings to talk about your progress and anything that may be holding you back - have you got all of the systems and equipment you need? Good luck.