If you have a data point where the error bars are a long way from the trendline, you should reexamine your data.
When you add a trendline to a chart with error bars, the line should go through all the error bars. If the line is not within the error bars, you probably have a problem. Either your error bars may not be big enough or you may have some unreliable data.
You can recalculate your error bars to see if that's where the error is, or you might have to go back to your experiment and examine the dubious data again.
Trendlines don't always go through all data points; this happens because of error values. Therefore, you can use error values and trendlines to test each other for validity.