When you've got a Pipeline like:

stage('foo') {
    node {
        withCredentials([string(credentialsId:'not-real', variable:'WHO_CARES')]) {
            echo "This will never happen."
        }
    }
}

You'll get a page like the attached screenshot - there's an error, specifically in withCredentials because I gave it a bogus credential ID - but since withCredentials isn't an atomic step, it's not represented on its own in the Blue Ocean UI. So it looks like no steps were run and there's nowhere to find the error!

In the second case, with a slightly different Pipeline:

stage('foo') {
    node {
        echo "splode"
        withCredentials([string(credentialsId:'not-real', variable:'WHO_CARES')]) {
            echo "This will never happen."
        }
    }
}

..there's a step that ran before the withCredentials block, so even though it actually succeeded, it's now marked as failed and there's still no way to find the actual log for the withCredentials error!