general the way it could work is you withhold some part of the data and you task a neural net to predict a bit with health portion from the remaining parts so this could be like you occlude some part of the image you look at the remaining pixels and you try to predict the occluded version or you have a video and you just hide some frames in the video you have the other frames and you try to fill in the blanks of the missing frames or you have a sentence and you mask out some words and you ask the neural network to fill in